feat: integrate Changesets for multi-package npm publishing

Migrate from single-bundle CLI publishing to publishing all @paperclipai/*
packages individually via Changesets. This fixes the "Cannot find package
@paperclipai/server" error when installing from npm.

Changes:
- Add @changesets/cli with fixed versioning (all packages share version)
- Make 7 packages publishable (shared, adapter-utils, db, 3 adapters, server)
- Add build scripts, publishConfig, and files fields to all packages
- Mark @paperclipai/server as external in CLI esbuild config
- Simplify CLI importServerEntry() to use string-literal dynamic import
- Add generate-npm-package-json support for external workspace packages
- Create scripts/release.sh for one-command releases
- Remove old bump-and-publish.sh and version-bump.sh
- All packages start at version 0.2.0

Usage: ./scripts/release.sh patch|minor|major [--dry-run]

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

package.json

@@ -17,12 +17,14 @@
     "db:backup": "./scripts/backup-db.sh",
     "paperclipai": "node cli/node_modules/tsx/dist/cli.mjs cli/src/index.ts",
     "build:npm": "./scripts/build-npm.sh",
-    "bump-and-publish": "./scripts/bump-and-publish.sh",
-    "version:bump": "./scripts/version-bump.sh",
+    "release": "./scripts/release.sh",
+    "changeset": "changeset",
+    "version-packages": "changeset version",
     "check:tokens": "node scripts/check-forbidden-tokens.mjs",
     "docs:dev": "cd docs && npx mintlify dev"
   },
   "devDependencies": {
+    "@changesets/cli": "^2.30.0",
     "esbuild": "^0.27.3",
     "typescript": "^5.7.3",
     "vitest": "^3.0.5"